Electroconductive polymeric materials such as polyacetylene, polypyrrole, and polyaniline are lighter in weight as compared with metals. In addition, they reveal high electroconductivity when anions or cations are doped, and they are thus electrochemically active. Taking advantage of such properties, they are now applied to electrochromic elements, various sensors, electrodes of batteries and the like.
However, when these electroconductive polymeric materials are employed for the above-mentioned electrodes, it is difficult to perform charge collection from these electroconductive polymeric materials. It may be possible to provide to these electroconductive polymeric materials with the function of a collector. However, it is more desirable to use the polymeric materials in combination with a collector for using the polymeric materials as electrodes, when the improvement of internal impedance and reliability of the electrodes is taken into consideration.
Polymeric active materials have an advantage in that they can readily be worked into a sheet. Therefore, it is desirable that a collector to be used in combination with the polymeric materials also be in the shape of a sheet.
Particularly, when the polymeric active materials are employed as an electrode of a battery, it is preferable to use a light and non-bulky collector in view of the energy density.
In the case of the above-mentioned structure, the close contact of the electrode active material and the collector is important to improve the charge collection efficiency. For this reason, various studies have been made of collectors for use in organic secondary batteries.
For instance, Japanese Laid-Open Patent Applications 58-115776 and 58-115777 disclose methods for achieving close contact between collectors and polymeric active materials. However, the polymeric active materials are poor in film-forming property and mechanical strength, so that the collector and the polymeric active material cannot be closely contacted with each other, and the active materials readily peel and fall off the collector during repeated charging and discharging. Consequently, the electrodes provided with such collectors and polymeric active materials have poor collecting efficiency and a short cycle life. Further, Japanese Laid-Open Patent Applications 62-20243 and 61-133557 disclose that electroconductive polymers can be subjected to electrochemical polymerization by employing a collector made of an expanded metal, wire netting or the like as an electrode. However, when a collector made of an expanded metal is used, it is hard to fully utilize the morphological characteristics of the conductive polymers, and the control of their morphology is also difficult. This is because it is considered that the morphology of each conductive polymer is determined by the diameter and the shape of the wire-like material. In addition, the above two-dimensional mesh-like metals are difficult to work into a thin sheet, especially into a sheet having a thickness of 50 .mu.m or less, so that they are not suitable for use as a collector of a sheet-shaped electrode for a thin battery. Furthermore, the electroconductive polymer characteristically grows around each wire material of the two-dimensional mesh-like structure, and it is difficult to cause the polymer to grow inside the lattices of the mesh-like structure. Even if the polymer grows inside the lattices, the polymer formed on the wire materials has a considerable thickness, so that an electrode having a uniform thickness is not obtainable.
It is therefore an object of the present invention to provide a composite sheet-shaped electrode comprising a collector and a polymeric material, with the collector and the polymeric material being very closely contacted with each other, which is light in weight and has high energy density and mechanical strength. Another object of the present invention is to provide a battery which is light in weight and has high energy density. A further object of the present invention is to provide a novel method of preparing a film of polymeric active material on a collector, thereby providing a method of producing a sheet-shaped electrode.
The inventors of the present invention have made earnest studies in order to solve the above described problems resided in the prior art. As a result, it was discovered that the problems can be solved by forming penetrating pores in a collector of a sheet-shaped electrode which is covered with a polymeric active material. The present invention has been accomplished based on the above discovery.
Further, the improvement in both the performance and the reliability of a battery has been achieved by using the above sheet-shaped electrode in the battery by use of a polymeric solid electrolyte in combination therewith, or by mounting the electrode in a specific manner. The present inventors have realized that the sheet-shaped electrode is usable in the various fields. For instance, when it is used as an electrode of a battery, the resulting battery shows high capacity and reliability. Particularly, a sheet-shaped thin type battery having the excellent properties has been successfully fabricated by using the sheet-shaped electrode together with a polymeric solid electrolyte or by mounting the sheet-shaped electrode in a specific manner.